1. CS 140 Lecture Notes: LinkersSlide 1 Memory Layout for Process Code 0 ∞ Data Stack

2. CS 140 Lecture Notes: LinkersSlide 2 Creating a Process Code 0 ∞ Data Stack 10101010 10101010 10101010 ccx.cx.sasx.o 10101010 10101010 10101010 ccy.cy.sasy.o 10101010 10101010 10101010 ccz.cz.sasz.o 10101010 10101010 10101010 Source Code Assembly Code Object Code Executable a.out CompilerAssemblerLinkerLoader ld OS

3. CS 140 Lecture Notes: LinkersSlide 3 A Simple Example extern float sin(); extern printf(), scanf(); main() { double x, result; printf("Type number: "); scanf("%f", &x); result = sin(x); printf("Sine is %f\n", result); } extern float sin(); extern printf(), scanf(); main() { double x, result; printf("Type number: "); scanf("%f", &x); result = sin(x); printf("Sine is %f\n", result); } main.c int printf(char *fmt,...) {... } int scanf(char *fmt,...) {... } int printf(char *fmt,...) {... } int scanf(char *fmt,...) {... } stdio.c double sin(double x) { static double res, lastx; if (x != lastx) { lastx = x; … compute sin(x) … } return res; } double sin(double x) { static double res, lastx; if (x != lastx) { lastx = x; … compute sin(x) … } return res; } math.c

4. CS 140 Lecture Notes: LinkersSlide 4 Object File extern float sin(); extern printf(), scanf(); main() { double x, result; printf("Type number: "); scanf("%f", &x); result = sin(x); printf("Sine is %f\n", result); } extern float sin(); extern printf(), scanf(); main() { double x, result; printf("Type number: "); scanf("%f", &x); result = sin(x); printf("Sine is %f\n", result); } main.cmain.o 20 32 40 56... call printf... call scanf... call sin... call printf def: main@T:0 ref: printf@T:20, T:56 ref: scanf@T:32 ref: sin@T:40... call printf... call scanf... call sin... call printf def: main@T:0 ref: printf@T:20, T:56 ref: scanf@T:32 ref: sin@T:40 text segment symbols relocation

5. CS 140 Lecture Notes: LinkersSlide 5 Object File double sin(double x) { static double res, lastx; if (x != lastx) { lastx = x; … compute sin(x) … } return res; } double sin(double x) { static double res, lastx; if (x != lastx) { lastx = x; … compute sin(x) … } return res; } math.cmath.o 8 20 204 0 8... load lastx... store lastx... load res res: lastx: def: sin@T:0 def: lastx@D:0 def: res@D:8 ref: lastx@T:8, T:20 ref: res@T:204... load lastx... store lastx... load res res: lastx: def: sin@T:0 def: lastx@D:0 def: res@D:8 ref: lastx@T:8, T:20 ref: res@T:204 text segment data segment relocation symbols

6. CS 140 Lecture Notes: LinkersSlide 6 After Pass 1 main.o text 0 64 276 700 math.o text stdio.o text math.o data 708 stdio.o data 836 main:0 sin:64 lastx:700 result:708 printf:314 scanf:508 Memory map:Symbol table:

7. CS 140 Lecture Notes: LinkersSlide 7 Relocation text segment in main.o 40... call 0... ref: sin@T:40 relocation record in main.o sin: 64 symbol table text segment in a.out 40... call 64...

8. CS 140 Lecture Notes: LinkersSlide 8